1. Field of the Invention
The present invention relates to improvements in three-piece freight car truck assemblies.
2. Description of the Prior Art
In a three-piece truck assembly, the side frames and bolster normally are square, i.e., the wheelsets and bolster (parallel to one another) are disposed normal to the side frames. Occasionally, however, at certain car speeds, the truck may become dynamically unstable, a phenomenon known as truck hunting, manifested by the truck going out of square or warping. The prior art teaches several ways of preventing truck hunting, e.g., the use of resilient side bearings, increasing warp stiffness, steering the wheelsets, the use of conconical wheel profiles, reducing lateral resistance, etc., and the literature has reported certain levels of warp stiffness achieved by three-piece truck assemblies. But numerous tests run to confirm the reported data show that warp stiffness of the levels reported by the literature cannot be achieved with known designs of three-piece freight car truck assemblies, and it appears that the reason for the lack of warp stiffness is instability of the wedges within the pockets.